Switching arrangement for electron microscopes



1941- H. o. MULLER 2,253,864

SWITCHING ARRANGEMENT FOR. ELECTRON MICROSGOPES Filed June 14, 1959 g wa ms I I F -J I 4a while Patented Aug. 26, 1941 SWITCHING ARRANGEMENT FOB ELECTRON MICBOSCOPES- Heinz Otto Miiller, Berlin- Spandau, Germany, assigner to Fides Gesellschaft fiir die Verwaltung und Verwertung von gewerblichen Schlitzrechten mit beschriinkter HaftuIm-Berlin, Germany, a corporation of Germany Application June 14, 1939, Serial No. 229,036

In Germany June 14, 1938 3 Claims.: 250-27) This invention relates to improvements in electron microscopes, and more particularly to an improved switching arrangement therefor. When projecting objects within so-called electron microscopes, foils consisting either of organic substances or of metal are usually employed as supports for the objects to be projected. Such foils must, of course, be extremely thin, since otherwise a considerable amount of electrons would be absorbed which would impair the quality of the electron optical image. Even when using the thinnest possible foils the electron optical'image is unfavorably influenced by the absorption of electrons if the current density in the plane of the object exceeds the permissible value. The current always attains a particularly high dfinsity if the focus of the condenser coil lies in t e plane of the object. When operating the seam microscope the electric and magnetic values are therefore selected in such a manner that the electron rays are focused behind or in front of the object. However, it has been found that the foils may then be destroyed owing to false switching operations when putting the electron microscope into operation.

To explain the difiiculties hitherto presented in electron microscopes reference may be had to the drawing, in which Fig. 1 is of explanatory nature and represents schematically part of an electron microscope,

Fig. 2 shows an arrangement according to the invention in connection with such a microscope. Fig. 1 shows an electron source 2', a magnetic condenser coil for focus-sing the beam of electron rays emitted from the electron source 2', and a foil 3' representing the object layer or carrying the object. In the operation of the microscope, the beam is so focussed that, as indicated by-full lines, the focal point lies outside of the plane of the foil 3. If the condenser coil were first to be switched in, when putting the electron microscope into operation and then the voltage of the ray were gradually to be increased to its full value, the electron rays would pass through or even remain some time in the focal condition indicated by broken lines where the focal point is in, or very close to, the plane of the foil 3' so that the foil is liable to be destroyed.

The invention eliminates this possibility with certainty.

-In an electron microscope according to the invention the switchingdevices for the individual current sources are designed and coupled with one another in such a manner that the condenser coil can be energized only after the full operating voltage is applied to the projecting electron ray. When employing a hot cathode as an electron source care must be taken to close at first the heating circuit for the hot cathode.

The switching devices of the electron microscope according to the invention may be interlocked or coupled in any suitable manner. Thus, for instance, it is possibleto attain the desired sequence of the switching operations with the aid of a controller drum type switch, as illustrated in Fig. 2.

In Fig. 2, I denotes an electron microscope; the.

. scope. A vacuum testing device I0 is connected to the electron microscope. II is a motor which moves the ground rod l2 in the upward and downward direction so that the high-voltage switch box 6 is grounded or insulated from ground.

To maintain the proper sequence of the switching operations, a rotary controller is employed consisting of the drum 13, shown developed in Fig. 2, which is provided with the contacts Hi to l9. These contacts cooperate with stationary contact pairs 20 to 25. Contact pair 20 is connected with the circuit of a signal lamp 26, the circuit also comprising a switch 21 which allows setting the signal circuit in and out of operation, and a suitable current source 28.

.Contact pair 2| is connected with the condenser coil 3 and a suitable voltage source 43. Contact pair 22 is connected with the primary winding 4| of the transformer 8 and its energizing voltage source 42. This primary transformer circuit is also controlled by a switch 31 which is series-- connected with the contact pair 20 and operated by the motor I I as set forth below. Contact pair 23 controls the energizing circuit of motor I], the power source of this motor circuit being designated by 36. Contact pair 24 is connected with a circuit including a power source 3| and a magnet coil 30 for actuating the switch I. The movable armature or core 32 of magnet coil 30 is linked to a bell crank lever journalled at 33' which has one arm 33 connected with the armature 32 and the other arm 35 with the switch I and is biased by a return spring 34 tending to keep the mechanism in the circuit-interrupting position. Coil 30, when energized, closes the switch 1 by attracting the armature 32 against the action of the spring 34. Finally, contact pair 25 is connected with the testing device l and its power source 29.

Fig. 2 shows the drum contactor in a switching position, indicated by I, wherein only the signal circuit of lamp 26 is closed. During the starting operation; the drum moves in the direction indicated by the arrow and passes in proper sequence through the switching positions indicated by II through VII. The signal lamp 26 is lighted during the entire switching procedure and extinguishes only after the final drum position VII is reached and the microscope I in proper working condition.

In the position II the contact pair 25 is bridged by the contact l9, thus connecting the vacuum testing device ill to the terminals 29 of the voltage source. As'soon as the vacuum has been tested, the drum switch is rotated into position III. In this position the contact pair 24 is bridged by the contact i8, thus connecting the exciting magnet 30 to the terminals 3! of the voltage source. The armature is drawn into the coil 30, so that the switch is closed and the cathode heating element inserted in the circuit and the Wehnelt-cylinder impressed with the desired voltage. The vacuum testing device I9 is deenergized in the switch position III and remains out of operation during the following steps IV to VII. In the switch position IV the contact pair 23 is bridged by the contact I1, thus energizing the motor ii. The motor ll actuates the switch rod H, by means of which the high-voltage side is grounded. The rod I2 is moved in a downward direction. The rod is provided with an extension 39 which cooperates with the switch 31. Upon the downward movement of the rod i2 the switch 31 closes its contact 40 under the action of the spring 38; the circuit for the lowvoltage winding 41 of the transformer 8 is thus prepared. This circuit upon passing into the switch position V is closed at the contacts 22, Hi.

In the position VI the voltage source 43 for the condenser coil 3 is inserted in the circuit by bringing the contacts 2i into engagement with the contact l5. By further rotating the drum l3 into the position VII the lamp 26 is finally disconnected. The microscope is now ready for making observations.

microscope, the switch drum 30 is rotated in the In order to disconnect the opposite direction, the above-described switching operations being eiIected in the reverse sequence.

What is claimed is:

1. An electron microscope having an irradiating device for emitting electron rays, means for energizing said irradiating device, said means comprising a low voltage primary circuit and a high voltage secondary circuit, in combination with high voltage switching means interposed between said secondary circuit and said irradiating device, low voltage switching means for controlling said primary circuit, further switching means connected with said condenser coil for controlling the energization of said coil, and a coupling connection between said different switching means for sequentially operating said diiIerent switching means so as to first close said secondary circuit and then energize said primary circuit to apply substantially the full operating voltage to said device before said coil is energized.

2. In combination with an electron miscroscope having an irradiating device for emitting electron rays and a condenser coil for i'ocussing said rays, a switching device for controlling the energizing voltage of said irradiating device, a second switching device for controlling the energization of said condenser coil, and connecting means disposed between said two switching devices for sequentially operating said devices so as to prevent said second switching device from energizing said coil before the operating voltage of said irradiating device is applied.

3. In an arrangement for electron-optically producing magnified images of objects, an electron microscope having an irradiating device for passing electron rays through the object, a supply circuit for energizing said device to emit a total ray energy of a magnitude injurious to the object if focussed thereon, and an electron-optical lens for biasing said electron rays, in combination with means for preventing said lens from focussing said rays onto the object, said means comprising a contact device for controlling said supply circuit of said irradiating device, a second contact device for controlling the energization of said lens, and interlocking means disposed between said contact devices for locking said second contact device in its inoperative position and unlocking it in dependence upon said first contact device so as to permit energizing said lens only after said irradiating device is under operating voltage.

HEINZ o'r'ro MtlLLER. 

